The production of hydraulic products or products with hydraulic potential from raw materials without emission of CO2 encounters difficulties inherent in their unfavourable chemistry and mineralogy for the production of a binding material.
By unfavourable is meant that the product obtained will not be usable on its own or optionally in a mixture with Portland cement because it will not show the resistance required by the standards or because it will generate problems relating to the swelling or destruction of the structures. This is the case for the LD scoriae(scoriae derived from solidified and crushed steel works slag).
The LD scoriae are by-products of the refining of haematite pig iron (smeltings poor in phosphorus) by the process of oxygen insufflation. This is a material rich in iron and lime having a mean mineralogical composition which is located in the set consisting of dicalcium silicates, calcium ferrite and metal oxides and the average chemical composition of the principal compounds of which is the following:
Compound% by weightCaO50SiO213Al2O33MgO6Iron oxides28Free ironUp to 20Free CaOUp to 10
The use of the LD scoriae in the form of granulates for concrete or for road construction for the generation of both bituminous upper layers and the foundation layers is limited by the presence of free lime which will create expansions of the road surface or of the concrete.
The transformation of the LD scoriae into a hydraulic binder also arouses much interest.
The patent FR-2.546.530 describes of steel works slag with a view to its use in cement.
The treatment described in this patent consists of adding to the liquid slag at least one compound capable of forming alumina, of supplying the quantity of heat necessary to dissolve the compound in the slag and of subjecting the slag to mixing with oxygen.
The quantity of the compound(s) capable of forming alumina added to the liquid slag is such that the treated slag contains 5 to 25% by weight of alumina.
Although the patent FR-2.546.530 indicates that the slag thus treated can be used as hydraulic binding material, in particularly for the manufacture of cement, this treatment does not make it possible to obtain a hydraulic binding material on its own, capable of replacing Portland cement entirely.
It has now been found that it is possible to treat steel works slag so as to confer on it a mineralogical composition lying in the range of specific mineralogical compositions such that the steel works slag thus treated constitutes a hydraulic binding material on its own, capable of replacing Portland cement entirely.